Lessons from temporal variation in the mammalian faunas from two collections of owl pellets in Columbia County, Washington

Collections of owl pellets deposited before and after a change in nearby habitats from producing wheat fields only to producing wheat fields and a patchy grass field were obtained from Columbia County, southeastern Washington. Pellets deposited before the change contained more than three times as many deer mice (Peromyscus maniculatus) as montane vole (Microtus montanus); pellets deposited after the change contained more than three times as many voles (M. montanus, M. longicaudus) as deer mice. The change in the ratio of deer mice to voles mirrors changes in rodent faunas in nearby areas caused by altered agricultural practices and resulting changes in vegetation. Because biologists correctly suggest the change in prey ratios could reflect variation in predation behaviours or prey availability, it is apparent that multiple lines of evidence are necessary to establish that changes in rodent faunas reflect changes in habitats.